In recent years, improvement in efficiency of an electric motor tends to be needed because of the increased awareness of saving energy. To meet this need, an electric motor that improve the efficiency by using the rotor having the permanent magnets inserted in the iron core, has been proposed.
In this electric motor, a torque ripple and an exciting force in the radial direction during the operation of the motor may increase because of an influence of a portion of the iron core on an outer peripheral side of the inserted permanent magnets. The torque ripple is pulsation caused by a change in the behavior of torque during the operation. The torque ripple causes vibration and noise, and it is therefore necessary to reduce of the torque ripple, as well as to improve the efficiency. In Patent Literature 1, a plurality of slits that are gaps is arranged at the portion of the iron core on the outer peripheral side of the inserted permanent magnets to thereby reduce the torque ripple.